The objective of this proposal is to use transgenic mice to understand the normal function of recoverin and to test whether its dysfunction will lead to retinopathy. A large body of evidence points to calcium as an important messenger in reestablishing the dark steady state, and recent biochemical analyses demonstrate that recoverin is a mediator of this calcium response. The physiological function of recoverin will be probed by introducing gain or loss of function into transgenic mice, and by introducing biochemically defined mutants into transgenic mice with disrupted recoverin genes. Specifically, targeted recoverin overexpression (gain of function) in the photoreceptor layer of transgenic mice will be achieved by using a characterized rhodopsin promoter to drive expression of the recoverin cDNA. Targeted gene disruption (loss of function) will be achieved by making homologous recombination in pluripotent embryonic stem (ES) cells and to use these cells to generate transgenic mice bearing disrupted recoverin genes. Recoverin mutants with defined biochemical defects will be introduced into transgenic mice with a null background, i.e. mice generated from the ES cells, to study specific mutant effects on phototransduction. The studies proposed here will contribute toward a better understanding of normal recoverin function and may also shed light on other visual processes which may be under calcium control. Interestingly, recoverin is the target antigen for autoantibodies formed in patients with caner-associated retinopathy (CAR). Significantly, sera from five out of five CAR patients tested contained antibody against recoverin. This striking correlation emphasizes the need to study the physiological role of recoverin in normal visual function and in retinopathies.